Additional costs for a prefabricated basement in a KfW40 house and a prefabricated basement

Hello,

I am considering building a KfW40 house approximately 8.5*11m with a basement. Some prefabricated house manufacturers say that the basement represents a big (financial) problem with KfW40 (and recommend KfW55), while for others it doesn’t seem to be a problem.

What additional costs can be expected for the basement?

Edit: Damn, I hit a key while editing the headline and now it can no longer be changed :-(

Maybe you start with an introduction thread and/or tell something about your property. It is difficult to say anything about cellars yes/no if you don’t know the background of the decision. Also, I don’t clearly see why you want to build [KfW40]. The fact is, if [KfW40], then this standard must be "fully implemented." That means if the cellar is to be included in the "thermal envelope," the cellar must practically be built to the [KfW40] standard as well. But those – meaning cellar yes/no and [KfW40] or [55] – are two questions that are hardly clarified without background information.

OK, that is of course an important piece of information. My plot is quite flat. I want to build a basement because I need storage space. I want to build KfW40 because, according to expert opinion, there is no big difference anymore compared to KfW55 and I get more funding there, also for a photovoltaic system.

I understand that the standard must be met. But that also applies to KfW55. Until now, or at the beginning, I always thought that it wouldn’t cause so many problems to raise the basement from KfW55 to KfW40. However, if there are massive additional costs, then I have two options: KfW55 with basement or build something slightly bigger as KfW40 without basement...

I want to build a basement because I need the storage space. I want to build KfW40 because there is no big difference anymore (according to expert opinion)

The expert opinion here is rather that the higher subsidy more or less only compensates the additional costs. In another thread you talk about a shelter, closing which could cover part of the storage space need (?)

Well researched. I had already considered continuing to use it. But somehow I changed my mind again. However, I haven't thought about closing it yet. Great idea, actually. However (now we’re straying a bit from the topic) I also want to build on the border with a carport followed by a closed building, in total already 9m of border development. If I close the patio, then enclosed space will also be created right on that border.

> more or less just offsets the additional costs.
Yes exactly, if the additional costs are covered, then I at least have lower ongoing costs. But you surely mean the additional costs only for the house and not the basement, right?

My question is whether the basement becomes extremely more expensive due to KfW40.

Of course, it becomes significantly more expensive, just as a house becomes much more expensive due to KfW 40. You must comply with the same conditions for the insulation as for the house.